Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $182.73   11.367%   $203.5009   $203.50   $203.50   $203.50  
  Purchase #2 $223.31   10.631%   $247.0501   $247.05   $247.05   $247.10  
  Purchase #3 $92.64   12.178%   $103.9217   $103.92   $103.90   $103.90  
  Purchase #4 $146.99   9.629%   $161.1437   $161.14   $161.15   $161.10  
  Purchase #5 $81.60   6.838%   $87.1798   $87.18   $87.20   $87.20  
  Purchase #6 $78.73   3.614%   $81.5753   $81.58   $81.60   $81.60  
  Purchase #7 $250.50   10.505%   $276.815   $276.82   $276.80   $276.80  
  7 purchase totals = $1,056.50       $1,161.1865   $1,161.19   $1,161.20   $1,161.20